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Introduce snapshot_vec abstraction

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This commit is contained in:
Niko Matsakis 2014-07-22 07:40:51 -04:00
parent 790d9c4708
commit d6e5797e41
4 changed files with 225 additions and 137 deletions
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1
src/librustc/lib.rs
View File

@ -136,6 +136,7 @@ pub mod util {
pub mod common;
pub mod ppaux;
pub mod nodemap;
pub mod snapshot_vec;
}
pub mod lib {

6
src/librustc/middle/typeck/infer/mod.rs
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@ -555,13 +555,13 @@ fn rollback_to(&self, snapshot: CombinedSnapshot) {
self.type_unification_table
.borrow_mut()
.rollback_to(self.tcx, type_snapshot);
.rollback_to(type_snapshot);
self.int_unification_table
.borrow_mut()
.rollback_to(self.tcx, int_snapshot);
.rollback_to(int_snapshot);
self.float_unification_table
.borrow_mut()
.rollback_to(self.tcx, float_snapshot);
.rollback_to(float_snapshot);
self.region_vars
.rollback_to(region_vars_snapshot);
}

160
src/librustc/middle/typeck/infer/unify.rs
View File

@ -16,9 +16,9 @@
use middle::typeck::infer::InferCtxt;
use std::cell::RefCell;
use std::fmt::Show;
use std::mem;
use syntax::ast;
use util::ppaux::Repr;
use util::snapshot_vec as sv;
/**
* This trait is implemented by any type that can serve as a type
@ -82,13 +82,8 @@ pub struct UnificationTable<K,V> {
/**
* Indicates the current value of each key.
*/
values: Vec<VarValue<K,V>>,
/**
* When a snapshot is active, logs each change made to the table
* so that they can be unrolled.
*/
undo_log: Vec<UndoLog<K,V>>,
values: sv::SnapshotVec<VarValue<K,V>,(),Delegate>,
}
/**
@ -96,29 +91,9 @@ pub struct UnificationTable<K,V> {
* made during the snapshot may either be *committed* or *rolled back*.
*/
pub struct Snapshot<K> {
// Ensure that this snapshot is keyed to the table type.
marker1: marker::CovariantType<K>,
// Snapshots are tokens that should be created/consumed linearly.
marker2: marker::NoCopy,
// Length of the undo log at the time the snapshot was taken.
length: uint,
}
#[deriving(PartialEq)]
enum UndoLog<K,V> {
/// Indicates where a snapshot started.
OpenSnapshot,
/// Indicates a snapshot that has been committed.
CommittedSnapshot,
/// New variable with given index was created.
NewVar(uint),
/// Variable with given index was changed *from* the given value.
SetVar(uint, VarValue<K,V>),
// Link snapshot to the key type `K` of the table.
marker: marker::CovariantType<K>,
snapshot: sv::Snapshot,
}
/**
@ -131,6 +106,8 @@ pub struct Node<K,V> {
pub rank: uint,
}
pub struct Delegate;
// We can't use V:LatticeValue, much as I would like to,
// because frequently the pattern is that V=Bounds<U> for some
// other type parameter U, and we have no way to say
@ -139,77 +116,26 @@ pub struct Node<K,V> {
impl<V:PartialEq+Clone+Repr,K:UnifyKey<V>> UnificationTable<K,V> {
pub fn new() -> UnificationTable<K,V> {
UnificationTable {
values: Vec::new(),
undo_log: Vec::new()
values: sv::SnapshotVec::new(Delegate),
}
}
pub fn in_snapshot(&self) -> bool {
/*! True if a snapshot has been started. */
self.undo_log.len() > 0
}
/**
* Starts a new snapshot. Each snapshot must be either
* rolled back or committed in a "LIFO" (stack) order.
*/
pub fn snapshot(&mut self) -> Snapshot<K> {
let length = self.undo_log.len();
debug!("{}: snapshot at length {}",
UnifyKey::tag(None::<K>),
length);
self.undo_log.push(OpenSnapshot);
Snapshot { length: length,
marker1: marker::CovariantType,
marker2: marker::NoCopy }
}
fn assert_open_snapshot(&self, snapshot: &Snapshot<K>) {
// Or else there was a failure to follow a stack discipline:
assert!(self.undo_log.len() > snapshot.length);
// Invariant established by start_snapshot():
assert!(*self.undo_log.get(snapshot.length) == OpenSnapshot);
Snapshot { marker: marker::CovariantType::<K>,
snapshot: self.values.start_snapshot() }
}
/**
* Reverses all changes since the last snapshot. Also
* removes any keys that have been created since then.
*/
pub fn rollback_to(&mut self, tcx: &ty::ctxt, snapshot: Snapshot<K>) {
debug!("{}: rollback_to({})",
UnifyKey::tag(None::<K>),
snapshot.length);
self.assert_open_snapshot(&snapshot);
while self.undo_log.len() > snapshot.length + 1 {
match self.undo_log.pop().unwrap() {
OpenSnapshot => {
// This indicates a failure to obey the stack discipline.
tcx.sess.bug("Cannot rollback an uncommitted snapshot");
}
CommittedSnapshot => {
// This occurs when there are nested snapshots and
// the inner is committed but outer is rolled back.
}
NewVar(i) => {
assert!(self.values.len() == i);
self.values.pop();
}
SetVar(i, v) => {
*self.values.get_mut(i) = v;
}
}
}
let v = self.undo_log.pop().unwrap();
assert!(v == OpenSnapshot);
assert!(self.undo_log.len() == snapshot.length);
pub fn rollback_to(&mut self, snapshot: Snapshot<K>) {
debug!("{}: rollback_to()", UnifyKey::tag(None::<K>));
self.values.rollback_to(snapshot.snapshot);
}
/**
@ -217,28 +143,12 @@ pub fn rollback_to(&mut self, tcx: &ty::ctxt, snapshot: Snapshot<K>) {
* can still be undone if there is a snapshot further out.
*/
pub fn commit(&mut self, snapshot: Snapshot<K>) {
debug!("{}: commit({})",
UnifyKey::tag(None::<K>),
snapshot.length);
self.assert_open_snapshot(&snapshot);
if snapshot.length == 0 {
// The root snapshot.
self.undo_log.truncate(0);
} else {
*self.undo_log.get_mut(snapshot.length) = CommittedSnapshot;
}
debug!("{}: commit()", UnifyKey::tag(None::<K>));
self.values.commit(snapshot.snapshot);
}
pub fn new_key(&mut self, value: V) -> K {
let index = self.values.len();
if self.in_snapshot() {
self.undo_log.push(NewVar(index));
}
self.values.push(Root(value, 0));
let index = self.values.push(Root(value, 0));
let k = UnifyKey::from_index(index);
debug!("{}: created new key: {}",
UnifyKey::tag(None::<K>),
@ -246,20 +156,6 @@ pub fn new_key(&mut self, value: V) -> K {
k
}
fn swap_value(&mut self,
index: uint,
new_value: VarValue<K,V>)
-> VarValue<K,V>
{
/*!
* Primitive operation to swap a value in the var array.
* Caller should update the undo log if we are in a snapshot.
*/
let loc = self.values.get_mut(index);
mem::replace(loc, new_value)
}
pub fn get(&mut self, tcx: &ty::ctxt, vid: K) -> Node<K,V> {
/*!
* Find the root node for `vid`. This uses the standard
@ -274,15 +170,7 @@ pub fn get(&mut self, tcx: &ty::ctxt, vid: K) -> Node<K,V> {
let node: Node<K,V> = self.get(tcx, redirect.clone());
if node.key != redirect {
// Path compression
let old_value =
self.swap_value(index, Redirect(node.key.clone()));
// If we are in a snapshot, record this compression,
// because it's possible that the unification which
// caused it will be rolled back later.
if self.in_snapshot() {
self.undo_log.push(SetVar(index, old_value));
}
self.values.set(index, Redirect(node.key.clone()));
}
node
}
@ -310,15 +198,12 @@ pub fn set(&mut self,
*/
assert!(self.is_root(&key));
assert!(self.in_snapshot());
debug!("Updating variable {} to {}",
key.repr(tcx),
new_value.repr(tcx));
let index = key.index();
let old_value = self.swap_value(index, new_value);
self.undo_log.push(SetVar(index, old_value));
self.values.set(key.index(), new_value);
}
pub fn unify(&mut self,
@ -359,6 +244,12 @@ pub fn unify(&mut self,
}
}
impl<K,V> sv::SnapshotVecDelegate<VarValue<K,V>,()> for Delegate {
fn reverse(&mut self, _: &mut Vec<VarValue<K,V>>, _: ()) {
fail!("Nothing to reverse");
}
}
///////////////////////////////////////////////////////////////////////////
// Code to handle simple keys like ints, floats---anything that
// doesn't have a subtyping relationship we need to worry about.
@ -373,7 +264,8 @@ pub trait SimplyUnifiable : Clone + PartialEq + Repr {
pub fn err<V:SimplyUnifiable>(a_is_expected: bool,
a_t: V,
b_t: V) -> ures {
b_t: V)
-> ures {
if a_is_expected {
Err(SimplyUnifiable::to_type_err(
ty::expected_found {expected: a_t, found: b_t}))

195
src/librustc/util/snapshot_vec.rs Normal file
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@ -0,0 +1,195 @@
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
* A utility class for implementing "snapshottable" things; a
* snapshottable data structure permits you to take a snapshot (via
* `start_snapshot`) and then, after making some changes, elect either
* to rollback to the start of the snapshot or commit those changes.
*
* This vector is intended to be used as part of an abstraction, not
* serve as a complete abstraction on its own. As such, while it will
* roll back most changes on its own, it also supports a `get_mut`
* operation that gives you an abitrary mutable pointer into the
* vector. To ensure that any changes you make this with this pointer
* are rolled back, you must invoke `record` to record any changes you
* make and also supplying a delegate capable of reversing those
* changes.
*/
use std::kinds::marker;
use std::mem;
#[deriving(PartialEq)]
enum UndoLog<T,U> {
/// Indicates where a snapshot started.
OpenSnapshot,
/// Indicates a snapshot that has been committed.
CommittedSnapshot,
/// New variable with given index was created.
NewElem(uint),
/// Variable with given index was changed *from* the given value.
SetElem(uint, T),
/// Extensible set of actions
Other(U)
}
pub struct SnapshotVec<T,U,D> {
values: Vec<T>,
undo_log: Vec<UndoLog<T,U>>,
delegate: D
}
pub struct Snapshot {
// Snapshots are tokens that should be created/consumed linearly.
marker: marker::NoCopy,
// Length of the undo log at the time the snapshot was taken.
length: uint,
}
pub trait SnapshotVecDelegate<T,U> {
fn reverse(&mut self, values: &mut Vec<T>, action: U);
}
impl<T,U,D:SnapshotVecDelegate<T,U>> SnapshotVec<T,U,D> {
pub fn new(delegate: D) -> SnapshotVec<T,U,D> {
SnapshotVec {
values: Vec::new(),
undo_log: Vec::new(),
delegate: delegate
}
}
fn in_snapshot(&self) -> bool {
!self.undo_log.is_empty()
}
pub fn record(&mut self, action: U) {
if self.in_snapshot() {
self.undo_log.push(Other(action));
}
}
pub fn push(&mut self, elem: T) -> uint {
let len = self.values.len();
self.values.push(elem);
if self.in_snapshot() {
self.undo_log.push(NewElem(len));
}
len
}
pub fn get<'a>(&'a self, index: uint) -> &'a T {
self.values.get(index)
}
pub fn get_mut<'a>(&'a mut self, index: uint) -> &'a mut T {
/*!
* Returns a mutable pointer into the vec; whatever changes
* you make here cannot be undone automatically, so you should
* be sure call `record()` with some sort of suitable undo
* action.
*/
self.values.get_mut(index)
}
pub fn set(&mut self, index: uint, new_elem: T) {
/*!
* Updates the element at the given index. The old value will
* saved (and perhaps restored) if a snapshot is active.
*/
let old_elem = mem::replace(self.values.get_mut(index), new_elem);
if self.in_snapshot() {
self.undo_log.push(SetElem(index, old_elem));
}
}
pub fn start_snapshot(&mut self) -> Snapshot {
let length = self.undo_log.len();
self.undo_log.push(OpenSnapshot);
Snapshot { length: length,
marker: marker::NoCopy }
}
fn assert_open_snapshot(&self, snapshot: &Snapshot) {
// Or else there was a failure to follow a stack discipline:
assert!(self.undo_log.len() > snapshot.length);
// Invariant established by start_snapshot():
assert!(
match *self.undo_log.get(snapshot.length) {
OpenSnapshot => true,
_ => false
});
}
pub fn rollback_to(&mut self, snapshot: Snapshot) {
debug!("rollback_to({})", snapshot.length);
self.assert_open_snapshot(&snapshot);
while self.undo_log.len() > snapshot.length + 1 {
match self.undo_log.pop().unwrap() {
OpenSnapshot => {
// This indicates a failure to obey the stack discipline.
fail!("Cannot rollback an uncommited snapshot");
}
CommittedSnapshot => {
// This occurs when there are nested snapshots and
// the inner is commited but outer is rolled back.
}
NewElem(i) => {
self.values.pop();
assert!(self.values.len() == i);
}
SetElem(i, v) => {
*self.values.get_mut(i) = v;
}
Other(u) => {
self.delegate.reverse(&mut self.values, u);
}
}
}
let v = self.undo_log.pop().unwrap();
assert!(match v { OpenSnapshot => true, _ => false });
assert!(self.undo_log.len() == snapshot.length);
}
/**
* Commits all changes since the last snapshot. Of course, they
* can still be undone if there is a snapshot further out.
*/
pub fn commit(&mut self, snapshot: Snapshot) {
debug!("commit({})", snapshot.length);
self.assert_open_snapshot(&snapshot);
if snapshot.length == 0 {
// The root snapshot.
self.undo_log.truncate(0);
} else {
*self.undo_log.get_mut(snapshot.length) = CommittedSnapshot;
}
}
}